When generating beam coverage patterns for a particular landmass, it is necessary to prevent interference from multiple radiated beams. This is particularly important when using a phased-array antenna system in which the beams are directed by phase shifters on each array element. Before generating each beam, an interference check must be performed so that the desired beam does not interfere with another beam that is being generated.
In a time-division multiple-access (TDMA) scheduling system, an interference check is commonly an integral portion of the TDMA scheduling algorithm.
In known beam interference check methods, one particular frequency, called the steering frequency f.sub.o, is chosen to be the frequency for which interference is checked. Commonly, the steering frequency is the center of the operating bandwidth of the signal to be transmitted or received. The phase shifts for each element given a steering direction (u.sub.o,v.sub.o) are calculated as: .phi..sub.m,n =(2.pi./.lambda..sub.o)d.sub.u mu.sub.o +(2.pi./.lambda..sub.o)d.sub.v nv.sub.o with .lambda.=c/f.sub.o, d.sub.u and d.sub.v is the inter-element spacings in u and v coordinate directions and for a given element location m,n. Other frequencies not equal to f.sub.o are derived by the ratio f/f.sub.o where f is the desired frequency.
One problem with the prior known method is that over a particular frequency width that is used for transmission, a phenomenon known as "beam squint" takes effect. For the operating frequency bandwidth, the circle footprints generated by the satellite beams from a particular phased-array element are slightly skewed from each other. That is, the position of beam at a frequency at the low end of the bandwidth will vary from the beam position of a beam at the high end of the bandwidth. Because beam squint is not taken into effect, undesirable interference may occur between beams generated from adjacent phased array elements.